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The Reason's for Evolution

The Basics:

Evolution,  noun

1. A gradual process in which something changes into a different and usually more complex or better form. See Synonyms at development.

2.    a. The process of developing.
       b. Gradual development.

3. Biology.

a. Change in the genetic composition of a population during successive generations, as a result of natural selection acting on the genetic variation among individuals, and resulting in the development of new species.
b. The historical development of a related group of organisms; phylogeny.

4.    A movement that is part of a set of ordered movements.
5.    Mathematics. The extraction of a root of a quantity.

The above definition is found from the online dictionary at www.dictionary.com. In biology this word defines a very simple concept, but one few people seem to understand. In the following essay I will explain this often misunderstood concept.

Evolution is not a magic process where species change gradually from one species to another, it does not follow any specific path nor does it have an ultimate end. Their is no "highest evolved" being.

Evolution works on two simple principals:
 

1. Organisms reproduce
2. The Organisms with the most favorable traits survive.

I don't think that there can be much argument on either of those two points, it's more than apparent that organisms reproduce. Obviously the organisms that have the most favorable traits to survive, do. One more note is that survival of an organism is only necessary before reproduction, after that the organism has already passed on its traits. Also note that organisms that are sterile (unable to reproduce) will not pass on any traits (again fairly obvious).

A Little Review of Genetics:

DNA (deoxyribonucliec acid) is shaped as a twisted ladder or double helix. On each side of the "ladder" are a sugar and a phosphate that build up the backbone. The rungs of the ladder are made up of opposing molecules called base pairs. In DNA there are four base pairs: Adenine, Guanine, Cytosine and Thymine. On the DNA stepladder, Adenine links to Thymine, and Cytosine links to Guanine. Two base pairs are linked together by hydrogen bonds. All of these base pairs are organic molecules made up of a combination of Carbon, Oxygen, Nitrogen, and Hydrogen.

Mitosis is the process where a somatic, or body cell reproduces. Meiosis is the process where gametic, or sex cells, reproduce. Metosis produces two daughter cells that split from the parent cell, and Meiosis produces four daughter cells that have half the chromosomes of the orignal cell.

A nucleotide is a phosphate, a sugar and a base hooked together. Basically the side of the ladder plus half a rung.

A gene is a stretch of bases in DNA that code for a protien. Protiens play a very important function in organisms.

To make a protien you must follow Transcription and Translation. In Transcription messenger ribonucleic acid (mRNA, a single sided "ladder, with the base pair Uracil in place of Thymine) copies a gene's information in DNA and takes it out to a ribosome. A ribosome holds the mRNA, and transcribes it to a protien.

How does DNA replicate? Imagine a single cell about to reproduce by mitosis. In order for the cell to reproduce, genetic information must be copied so that each daughter cell will have the crucial instructions it needs to sustain life. During DNA replication, special enzymes called helicases break away the base pairs and new nucleotides come in to fill in the spots on both sides. Gradually, more and more of each side is filled in until two complete strands of DNA are formed.

An Explanation of Variation:

In order for life to evolve, a variety of traits must be distributed amongst an organisms offspring. In sexual reproduction part of this is due to the fact that differing genetic material goes into the formation of the offspring. But both sexual and asexual reproduction have the common ability of mutation. Mutation occurs when genetic information is changed.

DNA mutates, causing different traits to occur in cells. A mutation is any change in DNA. Since a specific protien is made by a gene, if you change the bases found in a gene, the protein will change as well. This creates diversity in life.

So Why Do They Evolve?

Image a single bacteria cell. Bacteria cells have the ability to replicate as fast as once every twenty or thirty minutes. Using thirty minutes, let's see how many bacteria cells could be created in one week. Since there are 48 half hour periods in a day, and seven days in a week, there are 336 points where the bacteria(s) will reproduce. With the following pattern, multiplying the one bacteria by two, and then those two by two, in one week we'll have.  And the grand total: Over 8.749 X 10^99 Or if you want to see how big really it is:

8,749,002,899,132,047,697,490,008,908,470,500,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000

No, that's not exact, my calculator isn't that good. But just look at that number! Where do they all go? Obviously they can't all be living. How do they all find enough food and nutrients? The simple answer is they don't. A great deal of them will die, especially in an enviroment with only a limited number of food or space. Plain and simple, the ones with the best traits (caused by mutations) to  help them survive, will live.

So How Did it all Start?

This is the question that got me wondering the most, until I found my explanation. I highly recommend that you check out an excellent animation at http://vector.cshl.org/dnaftb.html, but I'll give you a brief explanation.

Many years ago the earth was a very inhospitable place. Acid rain and molten lava poured onto the earth, and there was no ozon to stip ultraviolet rays. Our atmosphere contain things like Ammonia (NH3), Carbon Dioxide (CO2), Hydrogen, and Methane (CH4). Notice these are all organic molecules.

In an experiment by the scientists Miller and Urey, a glass jar was created to simulate the conditions above. An upper chamber was made for the atmosphere, and a lower was made for the ocean. The matter was allowed to evaporate and condense through glass tubes. Gasses in the atmosphere were hit with electrical discharges, comparable to lightning in the earth's atmosphere. In another experiment UV rays were used in place of the electricity to produce the same results. Within a couple hours simple organic molecues were found at the top of the atmosphere. The molecules came down to the ocean chamber and then connected to make amino acids and other organic acids. Eventually nucleotides, sugars and other molecules crucial to life appeared.

Amino acids are able to form long chains, as are nucleotides (remember DNA?). Nucleotides attach to become RNA. That RNA may be used as a template for other nucleotides to line up. This process keeps occuring, the RNA copies itself, Life begins.

By odi_brassicium